19-year-old Mellor has been earmarked as one for the future at Crewe and was on the bench when the Alex travelled to Barnet in December altough he has yet to make a first team appearance he has been regular in the Academy.
Mellor can play at centre-half and right back but in recent months has been deployed as a holding midfielder in the Under-18's.
Mellor returned to his former club Nantwich Town back in October on a months loan.
The Castle who are top of the North West Counties Premier Division having only lost once all season secured a months loan with a view of extending it Castles secretary Ray Tatton told Newcastle's official site "Crewe were brilliant in the loan procedure and their contribution made it easy for me to get Kelvin on board in time for the Runcorn game. I would particularly like to thank Alison Bowler in getting the paperwork done in time and Neil Baker who liased with manager Greg Clowes to get the move up and running."